1. Field of the Invention
The present invention relates to a system and process used for visible light communication (VLC). More particularly, the present invention relates to a protocol for an interface of a wireless peripheral device that uses visible light as communication media.
2. Description of the Related Art
Recent advancements in the luminance efficiency of Light Emitting Diodes (LEDs) and a general price reduction for the costs of LEDs, has contributed to a wide spread increase in sales of LEDS for use in general lighting markets. In such general lighting markets, which include but are not limited to markets for the manufacture and sales of fluorescent lamps and incandescent lamps, as well as specific lighting markets, including markets of portable devices, displays, automobiles, traffic lights, billboards, etc., such markets have all had increased sales in the LED area.
In particular, white LEDs have now exceeded incandescent lamps in the luminance efficiency, and products using LEDS that are superior to fluorescent lamps have emerged. Recently, various factors (e.g. the exhaustion of RF band frequencies, potential crosstalk between several wireless communication technologies, an increasing demand for communication security, advent of an ultra-high speed ubiquitous communication environment based on 4G wireless technologies) have increased interest in radio over fiber technologies complementary to RF technologies. Therefore, research on visible light wireless communication employing visible light LEDs is now in progress by many enterprises and laboratories.
In the case of portable devices, such as, for example, a cellular phone and/or a PDA, and other small-sized digital appliances, including but not limited to as a digital camera and an mp3 (MPEG audio layer 3) player, considerable research has been already conducted for a peripheral interface performing inter-device communication using an Infrared Data Association (IrDA) module equipped therein, and related products have been developed and commercialized.
Unlike Radio Frequency (RF) communication, such as Bluetooth, Zigbee, etc., infrared wireless communication has several advantages in that it can achieve reliable security and lower power consumption without crosstalk between devices.
In view of the above-identified benefits associated with infrared wireless communication, there is an expectation that future local wireless communication systems will mainly employ a light-based scheme. Moreover, there has been a proposal to adopt a communication method based on visible light, rather than infrared light (i.e. IrDA modules), and a visible light-based scheme may be the main method of local communication in the future, especially considering the remarkable development in LED technology and better prices. One major difference between the visible light communication and other types of wireless RF communication lies in the fact that the user can recognize the data transmission/reception process and can visually check the communication security. In other words, the user can easily recognize not only the location of sending and receiving sides, but also the communication path.
FIG. 1A is a block diagram of the architecture of an infrared wireless interface in conventional infrared communication based on visible light.
The infrared communication protocol shown in FIG. 1A includes an upper layer, an Infrared Link Access Protocol (IrLAP) layer, an Encoder/Decoder (EnDec) layer, and a physical (TRx) layer. The IrLAP layer, also called a data link layer, performs particulars related to prescription of rules for accessing infrared media and procedures for communication schemes. The EnDec layer encodes or decodes original data to reduce error rates at the time of data transmission.
FIG. 1B is a view illustrating a frame exchange scheme adopted by the IrLAP layer in conventional infrared communications.
Referring to FIG. 1B, the frame architecture for data transmission includes at least one data frame required for data transmission from a sender to a receiver, at least one response frame needed by the receiver to inform the sender of a response regarding communication link establishment before the communication partner transmits data, and at least one acknowledge (ACK) frame for reporting a response regarding data transmission.
The data transfer path in transmission/reception processes as shown in FIG. 1B is as follows: the sender transmits a device discovery frame to the receiver, and then the receiver transmits a discovery response frame to the sender to respond to the transmitted frame and recognize the transmitting/receiving apparatus. Then, the sender sends a link negotiation frame to the receiver, and then the receiver sends a negotiation response frame to the sender to establish a link between the sender and the receiver. Then, the sender transmits a data frame containing actual data to the receiver via the established link, and the receiver transmits a data acknowledge frame to the sender to respond to the received data frame and perform data communication.
However, the conventional infrared communication scheme shown in FIG. 1B (half-duplex communication) has a problem in that, since no infrared ray is transmitted before a communication link is established, there is a long standby time after a short transmission until the reception process occurs. Such a phenomenon worsens when a link is established and when a temporarily disconnected link is restored.
Conventional infrared communication protocols have a problem in that, since no infrared ray is transmitted before a communication link is established, there is a long standby time after a short transmission until the reception process occurs. This means that, if a conventional infrared communication protocol is used for visible light communication, the user cannot align communication links through visual recognition of visible light.
Therefore, if visible light is used without modifying the infrared communication protocol, visibility is lost at the time of link connection and link restoration. That is, if the above-mentioned conventional infrared communication protocol is applied to visible light communication, the user cannot align communication links through visual recognition of visible light.